J 2 ECHINOIDEA. II. 



which inav throw aii\ lio^lit on tlie subject . Hut the stuch' of pedicellarias has onl\ added a new- 

 factor differino; in no \va\ in its potentialit> from those formerly in use , and there are several diffi- 

 culties to their use in classification. Like the other characters employed to distinguish the species 

 the\' varv with age. They form no exception and do not appear fnll\- fledged in the embryos and 

 \oung specimens, in spite of Dr. Mortensen's statement to the contrary-; though he acknowledges that 

 there is in literatme next to no more exact accounts of the development of the pedicellaria; of Echi- 

 noids.:; Cerlainh- before making such a sweeping use of the minute and often infinitesimal characters 

 supplied b\- pedicellarise for classification it would have been instructive to trace the development of 

 the several kinds of pedicellariee, and obtain some data regarding the extent and nature of the vari- 

 ation of pedicellarite during their growth. The only addition made b\ Dr. Mortensen to our know- 

 ledge of the development of pedicellaria; is shown on Figs. 15, 24, 30 PI. XII of the Ingolf Echinoidea, 

 giving three stages of a triphyllons pedicellaria of Phorinosoma placenta. As long as we know so little 

 regarding the nature of the relations of the large and the small pedicellarite of the same kind to one 

 another it seem useless to speculate on the improbabilitv ... of the arrangements- which must take 

 place in the calcareous mass to make a small fulh formed pedicellaria become a larger one . Every 

 student of Echini is fullv aware of the innuense amount of resorption and rearrangement constantly 

 taking place in the actiual and abactiual parts of the coronal plates in the interambnlacral areas, and 

 in the actinal and abactinal systems — changes that are far greater than those referred to above can 

 be\ — Further Professor Agassiz quotes my remark (p. 9): When no pronounced difference is found 

 between large and small pedicellaria;, it ma\ in fact be impossible to decide whether a certain speci- 

 men is to be regarded as a large or small form and adds that sureh this acknowledgement that 

 the pedicellari;e cannot be classified nia\ throw some doubt on the statement that the pedicellaria; 

 give absoluteh- excellent systematic characters (p. 106 — 7). 



In reph to these objections I cannot do better than refer to the remarks of Professor Doderleiu 

 (Op. cit. p. 67 -721. In a wa\- that could scarcely be l^etter or clearer the whole question is discussed 

 there, and w ith lull conviction I can subscribe to every word of it. < )nh a few remarks max be added. 

 I want to slate explicitly that I (pute agree with the remark thai the new factor (the pedicellarite) 

 differs in no way in its potentiality from those formerly in use ; it can never be said beforehand willi 

 certainty whether the pedicellaria; — or any other factor — are of primary importance in .some group 

 or not, only a careful comparative study can show ihe relative value of the different structural cha- 

 racter.s. I luue never stated that the classification has always to be based on the pedicellariit- as the 

 most important factor; on the contrar\, 1 am of oi)inion that where structural characters of some 

 .significance occur in the test, these are n])()ii ilie whole of higher cla.ssificatory value than the cha- 

 racters in the pedicellaria;. — The assertion thai the pedicellari;e do uol appear fulh fledged in the 

 embryos and \oung specimens in spite of Dr. M.'s statement to the contrary is quite unjustified. M\- 

 statement is not founded on the accounts thereof in literature b\il on uiv own fairly extensive studies; 

 and I would remark thai I do not .speak of the embryos in this connection but of the newly meta- 

 morphosed Echinoidv (p. 7). AH the different kinds of pedicellaria; may not perhaps be developed in 

 the very young specimens; but those forms which are found do not differ essentialh from those <if 

 the grown specimen.s, except iu size. Until it is proved 1)\ facts ijial llie pedicellariie of the Noung 



